Isotope effects on thermal diffusivity of boron carbide

Thermal diffusivities for the isotope-enriched samples, which are 10B4 12C, 10B4 13C, 11B4 12C and 11B4 13C, were measured by laser flash method over the temperature range from 290 to 1770 K. Thermal conductivity decreased with the molar weight of boron carbide. The heat transfer in boron carbide is considered to be mainly caused by acoustic phonons. As heavier isotopes were substituted for lighter ones, the phonon velocity in B4C decreased and so did the thermal conductivity. Consequently, total heat transfer by phonons is thought to decrease with molar weight.